Gas turbine engine combustion chambers experience extremely high temperatures in operation and the walls of the combustion chambers are generally cooled using a coolant.
It is known to provide combustion chambers comprising an inner wall and an outer wall or combustion chamber comprising segments, or tiles, and in particular the inner wall comprises a plurality of segments, or tiles, supported on the outer wall. The tiles consist of high temperature resistant material, e.g. a nickel base superalloy. The tiles are spaced from the inner surface of the outer wall to provide a passage for coolant. The outer wall of the combustion chamber may have apertures extending there-through to provide impingement cooling of the outer surfaces of the tiles. The tiles may have pedestals projecting from their outer surfaces to provide convection cooling of the tiles. The tiles may have apertures extending there-through to provide film cooling, or effusion cooling, of the inner surfaces of the tiles.
Each tile is generally mounted on the outer wall using studs which are integral with the tile and which extend through mounting apertures in the outer wall. The studs are generally threaded and washers and nuts are fastened onto the studs.
Our US patent U.S. Pat. No. 5,435,139 discloses an outer wall of a combustion chamber with apertures extending there-through to provide impingement cooling of the outer surfaces of the tiles and apertures extending through the tiles to provide film cooling, or effusion cooling, of the inner surfaces of the tiles.
Our US patent U.S. Pat. No. 6,857,275 discloses an outer wall of a combustion chamber with apertures extending there-through to provide impingement cooling of the outer surfaces of the tiles, pedestals projecting from the outer surfaces of the tiles to provide convection cooling of the tiles and apertures extending through the tiles to provide film cooling, or effusion cooling, of the inner surfaces of the tiles.
The upstream end of the outer wall of the combustion chamber is mounted on a combustion chamber casing and the downstream end of the outer wall of the combustion chamber is located in a slot in a discharge nozzle and a plurality of nozzle guide vanes are mounted on the discharge nozzle. In particular, if the outer wall is a radially outer wall of the combustion chamber it is located in a slot in a radially outer discharge nozzle and if the outer wall is a radially inner wall of the combustion chamber it is located in a slot in a radially inner discharge nozzle. The downstream end of the outer wall is generally provided with a machined cooling ring which has an axially extending flange arranged to locate in the slot in the corresponding discharge nozzle. The cooling ring has an axially, or an axially and radially, extending lip arranged generally parallel to the surface of the corresponding discharge nozzle. The cooling ring also has a plurality of apertures extending through the cooling ring to provide a coolant flow between the lip and the associated discharge nozzle to flow over the surface of the associated discharge nozzle and the nozzle guide vanes to protect the associated discharge nozzle and the nozzle guide vanes from the hot gases in the combustion chamber.
This arrangement has several problems. The cooling ring is manufactured from a machined forging, is heavy and is expensive to manufacture. The lip which extends from the cooling ring to direct the coolant from the apertures in the cooling ring over the surface of the discharge nozzle extends beyond the downstream ends of the tiles and hence may be exposed to the hot gases in the combustion chamber and may fail exposing the discharge nozzle to the hot gases in the combustion chamber. The segments, or tiles, with apertures extending there-through to provide film cooling of the inner surfaces of the segments, or tiles, are provided with peripheral walls to form a sealed cavity and these segments, or tiles, are not able to provide a flow of coolant over the lip of the cooling ring without compromising the efficiency of cooling of the segments, or tiles.
Therefore the present invention seeks to provide a novel combustion chamber arrangement which reduces or overcomes the above mentioned problem.